Internet protocol (IP) telephony employs several protocols to setup and manage calls and other types of sessions. One of the most widely adopted protocols for IP-based signaling is the Session Initiation Protocol (SIP). SIP is used for initiating new calls, manipulating call paths, and enabling the association of services with users regardless of their point of connection in the network. For example, SIP allows call forking, in which a single call can ring many endpoints at the same time. The use of SIP as an interface assures that clients and servers in an IP telecommunication system can rely on a common and widely used method for exchanging information.
The increasing use of SIP has spurred the development and introduction of numerous features using SIP interfaces for user and network access. For example, caller identification is one feature of SIP that can provide information about a caller to each device receiving a call request, allowing users receiving an incoming call to learn the identity of the caller before answering the call.